In recharging a battery, it is a common practice to supply a small current as the charging current over an extended period of time in order to reduce the effects of self-heating associated with the charging process. For example, in charging most lead acid batteries, a charge current rate of approximately 0.1 C is applied for most of the charging cycle in order to avoid overheating (“C” is used here in the sense of “C-rate,” a measurement of the charge/discharge capacity of a battery; for example, if a battery rated at 1 Ah (ampere-hour) is discharged at its 1C rate, it will provide 1 A for one hour, while at its 0.1 C rate, it will provide 0.1 A for ten hours). In contrast, if one attempts to use too high of a current early in the process of charging a battery, overheating can occur, which may cause damage to the battery. The drawback, however, to use of small current levels early in charging is that the battery is typically useless for a long period of time, due to the fact that it absorbs very little charge during the initial (low-current) charging period.
What is needed, therefore, is an improved battery charger that overcomes the shortcoming of having the battery be useless for such a long period of time at the beginning of the charge cycle.